# Population Dynamics of Ervilia castanea (Montagu, 1803) Hints at Evolutionary Processes Shaping North‐East Atlantic Insular Sandy Habitats

## TL;DR

The study explores how dynamic island environments shape the population genetics of a marine bivalve, revealing little genetic structure and unique genetic patterns.

## Contribution

The study provides new insights into the evolutionary processes and population dynamics of marine species in dynamic volcanic island habitats.

## Key findings

- Little to no genetic structure was observed between insular populations of Ervilia castanea.
- Insular populations showed deviations in Hardy–Weinberg Equilibrium, suggesting archipelago-specific processes.
- High dispersal ability and habitat transience likely lead to populations composed of multiple sources.

## Abstract

Volcanic oceanic islands are some of the Earth's most geologically and ecologically dynamic habitats, where continuous volcanic activity and erosion lead to the formation of habitats that drastically change throughout their ontogeny. No more so than shallow‐water sandy habitats, which repetitively disappear and regenerate due to seasonal oceanographic and climatic eustatic sea‐level variations. For their inhabitants, these events translate into populations being cyclically removed or experiencing drastic reductions in population size, where the outcome often depends on the specific life‐history modes of the species, determining their dispersal and colonization potential and, ultimately, their survival ability. Therefore, population genetic patterns of marine shallow‐water infaunal species can provide powerful clues to such outcomes, as well as how specific geological and ecological settings determine the genetic structure of the species. We herewith test the population structure of the marine infaunal bivalve
Ervilia castanea
(Montagu, 1803) in the sandy habitats of the Azores and Madeira Archipelagos (Northeast and Central Atlantic Ocean), by comparing insular populations with conspecifics from the nearest continental shores in mainland Europe. Little to no genetic structure was observed between insular populations with both nuclear microsatellites and the mitochondrial cytochrome c oxidase subunit I. Moreover, deviations in the Hardy–Weinberg Equilibrium of insular populations suggest the existence of archipelago‐specific processes. The high dispersal ability of
E. castanea
combined with the ephemeral nature of oceanic shallow‐water sandy habitats likely made each population composed of individuals from multiple sources. The high prevalence of null alleles and gene duplication hint at the potential occurrence of recent polyploidization events that require further investigation. Moreover, we found evidence of hyperdiversity among the markers used which may constrain the detection of more detailed patterns. We herewith demonstrate the uniqueness of insular environmental settings and inquire further into the evolutionary and biogeographic patterns of marine shallow‐water infaunal species from volcanic oceanic islands.

Shallow‐water sandy habitats of volcanic oceanic islands are among the most geologically and ecologically dynamic marine habitats on Earth. We investigate the population genetic patterns of
Ervilia castanea
, an infaunal marine bivalve with a planktotrophic larvae inhabiting Macaronesian shallow‐water sandy habitats. Little to no genetic structure was observed between insular populations alongside a unique genetic signature that inquires further investigation.